For decades, types of table tennis robots have been invented, patented, and manufactured These devices sequentially project table tennis balls from the machine side of the playing table (or playing court) to the top of the table on the players side at various time intervals and trajectories with different ball flying speeds and ball spinning rates for the player to practice As some examples, attention is directed to the following patents (U.S. Pat. Nos. 3,794,011, 4,116,438, 4,325,351, 4,917,380, 4,844,458, 5,009,421, 5,335,9054, 5,383,658, 5,485,995, 5,533,722, 6,186,132, 6,202,236, 6,371,872, 6,604,517, Chinese Patents Nos. 02217946, 03218645, 87214545, 93213663, 93244555, 94217832, 97240522, 98230401, 99207740)